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Climatic Information
Knowledge of Antarctica's climate is relatively recent, and detailed, long-term studies did not really start until the establishment of the first permanent scientific research stations, and especially the activities surrounding the International Geophysical Year of 1957-58. Nowadays, meteorological and related research is an important part of the work - sometimes the main work - of almost every station in the region and data is accumulating rapidly.
The main factors influencing the climate of Antarctica are the waters of the Southern Ocean, the seasonal variations of sea ice, the ice sheet that covers the continent itself, and its high altitude and high (southern) latitude. There are considerable climatological differences between the sea, the coastlines, and the interior. For instance, the Southern Ocean has most clouds, followed by Lesser Antarctica, while Greater Antarctica, with its high, arid plateau, has the least cloud cover. The key points to bear in mind are that Antarctica is extremely cold, dry, and windy, with little precipitation.
The Coldest Continent
First, Antarctica is the coldest continent. Mean temperatures in the interior during the coldest month (August) range from -40º to -70ºC (-40º to -94ºF) and in the warmest month (February) range from -15º to -45ºC (5º to -49ºF). The lowest outdoor temperature ever recorded on earth is -89.6ºC (-129.3ºF), which was recorded in 1983 at the Russian Vostok station on the inland ice cap. At sea level, Antarctic temperatures are some 10º-17ºC (50º-63ºF) colder than the Arctic.Nevertheless, there are considerable variations. At the sub-Antarctic islands, for example, temperatures may range from about -40ºC in midwinter (August) to +14ºC in January or February (-40º to +57ºF).
The Windiest Continent
Antarctica is also the windiest of the continents. Apart from global wind currents, Antarctica actually creates its own wind systems. Cold dense air essentially slides from the high interior ice fields towards the lower areas along the coasts. At the edges of the ice plateau the winds accelerate, thereby lifting and blowing clouds of snow high into the air. The strongest winds are habitually found on the long coastal slopes of Greater Antarctica.
Some coastal areas endure almost constant strong winds, whereas other areas may be quite calm much of the time and then suddenly experience hurricane force winds as air rushes down through glacial valleys. These sudden and unexpected winds are called katabatic, or down slope, winds. The famous Australian explorer Douglas Mawson established a base at Cape Denison, Commonwealth Bay, in 1912 and recorded wind speeds for two years. This is reputed to be the windiest place on earth, because the average wind speed during that period was 72 kilometers per hour (45 miles per hour), and gusts of more than 240 kph (150 mph) were common. Nevertheless, wind speeds have been observed to drop very significantly just a few miles away from the coast.
Visitors to Antarctica should be aware that katabatic winds can occur quite suddenly, and with little warning, but then die down again just as quickly. They create dramatically low effective temperatures, due to the wind-chill factor. In the Southern Ocean, strong gale-force winds are quite common, especially in the region between 40º-60ºS. These cyclonic storms are caused by extremely cold air coming from Antarctica meeting the relatively warm and moist air over more northerly seas. This accounts for the fearsome reputation of the Drake Passage. The storms tend to circle Antarctica from west to east.
The Driest Continent
Surprisingly, Antarctica is the driest continent. By definition, most of the continent is a desert. There is very little precipitation each year in the interior, and the vast amount of ice and snow which make up the polar ice cap has accumulated over many millions of years. The mean annual accumulation for the entire continent amounts to less than five centimeters (two inches) of water equivalent, which is just slightly more than that of the Sahara Desert.
But some coastal areas, particularly the west side of the Antarctic Peninsula, receive much more precipitation. The tip of the peninsula receives about 90 centimeters (35 inches) of water equivalent each year. Here and in the South Shetland Islands it may rain, sometimes quite heavily - a typical maritime climate.
Despite what has been said in this section, visitors to the Antarctic Peninsula region need not expect to experience very bad weather as a matter of course. Crossings of the Southern Ocean can be quite easy and severe storms are infrequent in the southern summer months. The narrow waterways of the Antarctic Peninsula are quite protected. Likewise, sunny days are rather common in Greater Antarctica and the sun even shines among the subantarctic islands and Antarctic Peninsula . Although visitors should be prepared for cold weather at any time, it is surprising how often it can seem almost too warm to wear a parka. The average summer temperature is near freezing.
The Antarctic Circle
It is interesting to understand the significance of the Antarctic Circle and its relation to the hours of daylight. As you travel farther south in the austral summer months, the days get progressively longer. The Antarctic Circle is located at about 66º33'S (its position varies very slightly from year to year, as the earth wobbles about its axis). This circle marks the northernmost point at which the sun is visible for 24 hours a day at the summer solstice, on December 21, when it is at its highest point above the horizon.
Before that date, the sun is still climbing toward its zenith, and afterwards it is descending, so if you reach this region before or after December 21, you would need to sail farther south of the Antarctic Circle to experience a 24-hour day. (Exactly the same - but opposite - process occurs in the northern hemisphere, of course, so that the relevant date applicable to the Arctic Circle is June 21.)
Four Different Poles
The South Pole that is referred to in everyday conversation is in fact the Geographical South Pole, which is the southernmost end of the earth's rotational axis (the earth rotates around a line, or axis, drawn between the north and south geographical poles). But there are three other "poles" which are of interest to scientists.
The Magnetic South Pole is where the lines of force of the earth's magnetic field converge. The position of this pole is constantly moving, by some 10-20 kilometers per year, due to variations in the earth's magnetic field. Ships' navigation officers have to take into account this magnetic variation when interpreting their compass readings. The magnetic south pole is currently (1997) located off Adélie Land, in the French sector of Antarctica, in the general vicinity of the Dumont d'Urville station.
The Geomagnetic South Pole is a theoretical definition used to rationalize variations in the earth's magnetic field. It is located at latitude 78º05'S, longitude 111ºE, in the Australian sector near the Russian Vostok station.
The Pole of Relative Inaccessibility is the center of the continent as measured by its distance from the coasts. It is located at latitude 82º06'S, longitude 54º58'E, also in the Australian sector.
Copyright © Nigel Sitwell & Tom Ritchie / Quark / Terra Mater Expedições